A cellular communication device typically uses a removable subscriber identifier module (SIM) that configures and authorizes the device for use on a cellular communication network. Among other information, a SIM stores the identity and phone number of the subscriber. The subscriber identity is represented by a code that is referred to as an international mobile subscriber identity (IMSI) number. Each SIM also identifies the network with which the SIM is associated and which will be the home network of the device in which the SIM is installed.
For 5th-Generation (5G) cellular networks, there is a desire to conceal the subscriber identity. Specifically, 5G networks are to avoid sending unencrypted subscriber identifiers over the radio access network (RAN), to prevent hackers from obtaining the subscriber identifiers.
5G Technical Specifications (3GPP TS 33.501) set forth a protocol for storage and transmission of subscriber identifiers. In accordance with these protocols, a subscriber's identity is represented as a globally unique subscription permanent identifier (SUPI) stored in the subscriber's SIM. The SUPI contains the IMSI and other information. Rather than sending the unencrypted SUPI over the air, the SUPI is encrypted using a public encryption key of the home network associated with the SIM. The encryption may be performed either by the SIM itself or by the communication device to create a concealed subscriber identifier referred to in 5G specifications as a subscription concealed identifier (SUCI). The SUCI is used when authenticating with 5G networks.